This invention generally relates to an improved catalyst for the conversion of hydrocarbons. More specifically, this invention relates to a reforming catalyst for the catalytic reforming of gasoline-range hydrocarbons that results in increased aromatics production.
The subject of the present invention is a novel dual-function catalyst, characterized by a multimetallic combination of three or more metal components in specified concentrations on the finished catalyst, and its use in hydrocarbon conversion with increased aromatics production. Catalysts having both a hydrogenation-dehydrogenation function and a cracking function are used widely in many applications, particularly in the petroleum and petrochemical industry, to accelerate a wide spectrum of hydrocarbon-conversion reactions. The cracking function generally relates to an acid-action material of the porous, adsorptive, refractory-oxide type which is typically utilized as the support or carrier for a heavy-metal component, such as the Group VIII (IUPAC 8-10) metals, which primarily contribute the hydrogenation-dehydrogenation function. Other metals in combined or elemental form can influence one or both of the cracking and hydrogenation-dehydrogenation functions.
In another aspect, the present invention comprehends improved processes that emanate from the use of the novel catalyst. These dual-function catalysts are used to accelerate a wide variety of hydrocarbon-conversion reactions such as dehydrogenation, hydrogenation, hydrocracking, hydrogenolysis, isomerization, desulfurization, cyclization, alkylation, polymerization, cracking, and hydroisomerization. In a specific aspect, an improved reforming process utilizes the subject catalyst to increase selectivity to gasoline and aromatics products.
Catalytic reforming involves a number of competing processes or reaction sequences. These include dehydrogenation of cyclohexanes to aromatics, dehydroisomerization of alkylcyclopentanes to aromatics, dehydrocyclization of an acyclic hydrocarbon to aromatics, hydrocracking of paraffins to light products boiling outside the gasoline range, dealkylation of alkylbenzenes and isomerization of paraffins. Some of the reactions occurring during reforming, such as hydrocracking which produces light paraffin gases, have a deleterious effect on the yield of products boiling in the gasoline range. Process improvements in catalytic reforming thus are targeted toward enhancing those reactions effecting a higher yield of the gasoline fraction at a given octane number.
It is of critical importance that a dual-function catalyst exhibits the capability both to initially perform its specified functions efficiently and to perform them satisfactorily for prolonged periods of time. The parameters used in the art to measure how well a particular catalyst performs its intended functions in a particular hydrocarbon reaction environment are activity, selectivity and stability. In a reforming environment, these parameters are defined as follows: (1) Activity is a measure of the ability of the catalyst to convert hydrocarbon reactants to products at a designated severity level, with severity level representing a combination of reaction conditions: temperature, pressure, contact time, and hydrogen partial pressure. Activity typically is designated as the octane number of the pentanes and heavier (“C5+”) product stream from a given feedstock at a given severity level, or conversely as the temperature required to achieve a given octane number. (2) Selectivity refers to the percentage yield of petrochemical aromatics or C5+ gasoline product from a given feedstock at a particular activity level. (3) Stability refers to the rate of change of activity or selectivity per unit of time or of feedstock processed. Activity stability generally is measured as the rate of change of operating temperature per unit of time or of feedstock to achieve a given C5+ product octane, with a lower rate of temperature change corresponding to better activity stability, since catalytic reforming units typically operate at relatively constant product octane. Selectivity stability is measured as the rate of decrease of C5+ product or aromatics yield per unit of time or of feedstock.
Some catalysts may have both a hydrogenation-dehydrogenation function and a cracking function and are useful for accelerating a wide spectrum of hydrocarbon-conversion reactions. Different components, such as the carrier, may contribute to the cracking function while other portions, such as deposited metals, may contribute to the hydrogenation-dehydrogenation function. Some components contribute to both the cracking and hydrogenation-dehydrogenation functions. Typically, dual function catalysts are used to accelerate a variety of hydrocarbon conversion reactions, such as dehydrogenation, hydrogenation, hydrocracking, hydrogenolysis, isomerization, desulfurization, cyclization, alkylation, polymerization, cracking, and hydroisomerization.
Generally, it is desirable to have flexibility with catalyst functionality for utilizing in various processes, such as reforming. In one exemplary reforming process, increasing the yield of one or more C5+ hydrocarbons, hydrogen, and aromatic yields is desired. Optionally, the acidity of the catalyst can be altered by adding a metal and/or other elements to the catalyst. Generally, modification of the acid function results in reduced cracking of the alkanes to C3 and C4 light ends allowing increased selectivity to the formation of aromatics. Modification of the metal function may also occur resulting in the reduction of alkane cracking to methane and ethane. There can also be a reduction in the dealkylation reactions of aromatics leaving heavier and more valuable C8+ aromatics.
Beside the yields, the activity of a catalyst may enable obtaining a commercially useful conversion level without employing additional quantities of catalyst or using excessively high temperatures, which can lead to undesired higher costs. Higher catalyst activity can also be utilized to process greater quantities of feed or to increase conversion, and therefore increase the production of valuable products.
This invention relates to new catalytic materials that are more selective towards reforming of naphtha feeds compared to those in the art. In one embodiment, the catalytic material comprises a refractory aluminum oxide support, a metal from the platinum group, tin, a halogen element, at least one lanthanide element and one or more alkali metals from Group 1, or one or more alkaline earth metals from Group 2, or mixtures thereof of Group 1 and Group 2 metals. A catalyst with a combination of a lanthanide metal and alkali metals, such as, Li, Na, K, was unexpectedly found to be more selective towards aromatics compared to reference reforming catalysts.